EP0730344A1 - Single pole negative feedback for class-D amplifier - Google Patents
Single pole negative feedback for class-D amplifier Download PDFInfo
- Publication number
- EP0730344A1 EP0730344A1 EP95830063A EP95830063A EP0730344A1 EP 0730344 A1 EP0730344 A1 EP 0730344A1 EP 95830063 A EP95830063 A EP 95830063A EP 95830063 A EP95830063 A EP 95830063A EP 0730344 A1 EP0730344 A1 EP 0730344A1
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- EP
- European Patent Office
- Prior art keywords
- input
- circuit
- node
- amplifier
- output
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 239000010752 BS 2869 Class D Substances 0.000 title 1
- 239000003990 capacitor Substances 0.000 claims abstract description 6
- 230000008878 coupling Effects 0.000 claims abstract description 4
- 238000010168 coupling process Methods 0.000 claims abstract description 4
- 238000005859 coupling reaction Methods 0.000 claims abstract description 4
- 238000010586 diagram Methods 0.000 description 3
- 230000005236 sound signal Effects 0.000 description 3
- 230000003321 amplification Effects 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 238000003199 nucleic acid amplification method Methods 0.000 description 2
- 101000895635 Dictyostelium discoideum CAR1 transcription factor Proteins 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000004513 sizing Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/08—Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements
- H03F1/083—Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements in transistor amplifiers
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
- H03F3/21—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers with semiconductor devices only
- H03F3/217—Class D power amplifiers; Switching amplifiers
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K7/00—Modulating pulses with a continuously-variable modulating signal
- H03K7/08—Duration or width modulation ; Duty cycle modulation
Definitions
- This invention relates to D-class or two-state amplifiers, and more particularly to a D-class amplifier adapted to be integrated monolithically for use in applications of the audio type.
- a particular requirement of such applications is that the efficiency of the audio amplifiers be improved over that of conventional B- or AB-class stages, without in any way penalizing it with the possible introduction of harmonic distortion.
- D-class amplifiers in which active power circuit elements are used, such as switches which are alternately driven to saturation and cut-off at a high switching speed.
- D-class amplifiers provide, prior to the amplification proper, for the encoding of the information or audio signal by a particular pulse modulation system.
- the required analog signal for driving the loudspeaker is then obtained by appropriate filtering downstream of the final stage of the amplifier.
- the modulation step converts the audio signal to be amplified into a sequence of pulses of the square waveform type, whose basic characteristic is that its time duration is proportional to the instant amplitude of the input signal.
- PWM Pulse-Width Modulation
- the resultant signal having a much different waveform from the original one, is complete with all the information.
- a major limiting factor to the use of two-state amplifiers in audio applications is that the distortion introduced into the audio signal may not be consistent with a high quality of sound reproduction, unless special measures are taken, such as very high switching rates, which add to the system complexity, however.
- the demodulation filter downstream from the amplifier is typically an LC filter, i.e. a low-pass filter having a greater number of poles than one.
- FIG. 1 of the drawings appended to this specification is a block diagram of the classic solution used by the skilled ones in the art, wherein the negative feedback is tapped off downstream from the demodulation filter.
- the feedback loop must also be provided with some suitable compensation because, as mentioned above, the demodulation filter has at least two poles.
- Figure 2 of the drawings shows a different way of obtaining an oscillator which automatically has a degree of feedback.
- the underlying technical problem of this invention is to provide an amplifier of the negative feedback, two-state type which can provide low harmonic distortion and high stability using very simple circuitry.
- Shown in Figure 3 is a general scheme for a negative feedback, D-class or two-state amplifier, according to the invention wherein individual blocks are used to also indicate the demodulation filter downstream from the amplifier and a load, which may be a loudspeaker in audio applications.
- the D-class amplifier AMP-D has first IN1 and second IN2 input terminals for coupling to a signal source, and an output terminal OUT through which a pulse modulated signal is transferred to the low-pass filter for demodulation into an analog load drive signal.
- a first resistor R1 is feedback connected between the output terminal OUT and an input node N of the amplifier.
- a second resistor R2 is connected between that node N and the second input terminal IN2.
- a capacitor of suitable capacitance is also connected between the first input terminal IN1 and the input node N.
- first and second circuit elements with a predetermined impedance, plus a suitable capacitive element may be used to meet specific design requirements.
- the open loop gain A 0 of a D-class amplifier can be regarded, in fact, to be virtually constant in frequency for frequency values f i of the input signal which are below the switching frequency f sw , and there are no significant poles.
- the capacitor C is placed between ground and a virtual ground, and therefore, no signal current will be flowed through it; gain has, in fact, the value of -R1/R2 regardless of the value of its capacitance.
- V 0 ⁇ A 0 ⁇ Vd
- Figure 4 shows a very simple circuit diagram which allows the pulse modulation of an analog signal to be carried out.
- the feedback D-class amplifier of this invention includes a differential input structure comprised of two transistors, T1 and T2, and a constant current generator G.
- the two output legs of the differential structure are connected to the inputs, S and R, of a bistable multivibrator MVIBR which is driven by the varying currents through the two legs to generate a pulse modulated output signal.
- An active power element level-translating circuit RSW outputs a square waveform signal PWM capable of powering the load.
- a frequency compensator CRTF which functions to keep the switching constant.
Abstract
Description
- This invention relates to D-class or two-state amplifiers, and more particularly to a D-class amplifier adapted to be integrated monolithically for use in applications of the audio type.
- A particular requirement of such applications is that the efficiency of the audio amplifiers be improved over that of conventional B- or AB-class stages, without in any way penalizing it with the possible introduction of harmonic distortion.
- This requirement originates from that there exists a limitation to the power dissipation of an audio amplifier of the conventional monolithically integrated type.
- A solution to this problem is provided by D-class amplifiers in which active power circuit elements are used, such as switches which are alternately driven to saturation and cut-off at a high switching speed.
- While the operation of traditional amplifiers is limited to increasing the voltage and current of input signals without significantly altering their waveforms (unless saturation phenomena make their appearance), D-class amplifiers provide, prior to the amplification proper, for the encoding of the information or audio signal by a particular pulse modulation system.
- The required analog signal for driving the loudspeaker is then obtained by appropriate filtering downstream of the final stage of the amplifier.
- The modulation step converts the audio signal to be amplified into a sequence of pulses of the square waveform type, whose basic characteristic is that its time duration is proportional to the instant amplitude of the input signal.
- This type of pulse modulation is also known as PWM (Pulse-Width Modulation), and affords very high efficiency levels, in principle of up to 100%.
- The resultant signal, having a much different waveform from the original one, is complete with all the information.
- The D-class or two-state amplification technique is well known to the skilled ones in the art, and the problems it involves are dealt with, for example, in an article "Modulated Pulse Audio Power Amplifiers for Integrated Circuits" by H.R. Camenzind, IEEE Transactions on Audio and Electroacoustics, Vol. AU-14, No. 3, September 1966.
- A major limiting factor to the use of two-state amplifiers in audio applications is that the distortion introduced into the audio signal may not be consistent with a high quality of sound reproduction, unless special measures are taken, such as very high switching rates, which add to the system complexity, however.
- In addition, the demodulation filter downstream from the amplifier, as indispensable for driving the load, is typically an LC filter, i.e. a low-pass filter having a greater number of poles than one.
- In order to reduce distortion and offset, it is therefore necessary that a negative feedback be provided in the system.
- Shown in Figure 1 of the drawings appended to this specification is a block diagram of the classic solution used by the skilled ones in the art, wherein the negative feedback is tapped off downstream from the demodulation filter.
- However, the feedback loop must also be provided with some suitable compensation because, as mentioned above, the demodulation filter has at least two poles.
- This technique is described, for instance, in an article P.C1-1C1-31 by the Unitrode Power Supply Design Seminar (SEM-700).
- Figure 2 of the drawings shows a different way of obtaining an oscillator which automatically has a degree of feedback.
- This solution is described in US Patent No. 3,294,981 to Bose; it is not capable, however, of suppressing distortions brought about by the integrator which forms the filter being less than ideal.
- A more recent solution to the problem of the dual pole of the demodulation filter is disclosed in another US patent to Bose (No. 4,456,872), whereby a D-class amplifier with current feedback is provided.
- In practicing this solution, however, a disadvantage is that small signals are to be processed, with attendant sensitivity to noise and switching glitch.
- The underlying technical problem of this invention is to provide an amplifier of the negative feedback, two-state type which can provide low harmonic distortion and high stability using very simple circuitry.
- This problem is solved by a negative feedback D-class amplifier as previously indicated and defined in the characterizing portion of the appended claims to this specification.
- The features and advantages of a two-state amplifier according to the invention will be apparent from the following description of an embodiment thereof, given by way of example and not of limitation with reference to the accompanying drawings.
- In the drawings:
- Figures 1 and 2 show block diagrams of the known technical solutions discussed hereinabove;
- Figure 3 shows a general scheme for a negative feedback two-state amplifier according to the invention; and
- Figure 4 shows a preferred embodiment of that general scheme.
- Shown in Figure 3 is a general scheme for a negative feedback, D-class or two-state amplifier, according to the invention wherein individual blocks are used to also indicate the demodulation filter downstream from the amplifier and a load, which may be a loudspeaker in audio applications.
- It matters to observe that the feedback topology shown is a universal one, and accordingly applicable to the amplifier regardless of its implementation circuit-wise and of its application.
- The D-class amplifier AMP-D has first IN1 and second IN2 input terminals for coupling to a signal source, and an output terminal OUT through which a pulse modulated signal is transferred to the low-pass filter for demodulation into an analog load drive signal.
- A first resistor R1 is feedback connected between the output terminal OUT and an input node N of the amplifier.
- A second resistor R2 is connected between that node N and the second input terminal IN2.
- In accordance with the invention, also connected between the first input terminal IN1 and the input node N is a capacitor of suitable capacitance.
- More generally, first and second circuit elements with a predetermined impedance, plus a suitable capacitive element, may be used to meet specific design requirements.
- With a D-class amplifier fed back in accordance with this novel topology, the following results can be obtained:
the loop gain has a single pole (
the pole of the loop gain can be arranged, at the designing stage, to be within the audio frequency band, without affecting the frequency response of the amplifier but advantageously reducing the residual ripple caused by the output square wave and being input back by the feedback. - This can be readily verified by a skilled one in the art.
- The open loop gain A0 of a D-class amplifier can be regarded, in fact, to be virtually constant in frequency for frequency values fi of the input signal which are below the switching frequency fsw, and there are no significant poles.
-
- If a configuration of the inverting type is considered, also in connection with the scheme of Figure 3, that is one where the input terminal IN2 is regarded as the inverting input terminal of the operational, to which the input signal Vi is applied while IN1 is connected to a ground, and if the open loop gain A0 is sufficiently high, then the circuit node N can be regarded to be a virtual ground for the signal, and since the input current
- The capacitor C is placed between ground and a virtual ground, and therefore, no signal current will be flowed through it; gain has, in fact, the value of -R1/R2 regardless of the value of its capacitance.
-
-
-
- Figure 4 shows a very simple circuit diagram which allows the pulse modulation of an analog signal to be carried out.
- The feedback D-class amplifier of this invention includes a differential input structure comprised of two transistors, T1 and T2, and a constant current generator G.
- The two output legs of the differential structure are connected to the inputs, S and R, of a bistable multivibrator MVIBR which is driven by the varying currents through the two legs to generate a pulse modulated output signal.
- An active power element level-translating circuit RSW outputs a square waveform signal PWM capable of powering the load.
- Also shown in the Figure is a frequency compensator CRTF, which functions to keep the switching constant.
- It should be understood that the embodiment described hereinabove for purely illustrative purposes is susceptible of modifications, integrations and substitutions of its elements without departing from the protection scope of the following claims.
Claims (4)
- A power amplifier (AMP-D) of the two-state type, comprising a modulation circuit operative to convert an electric input signal to a pulse signal of the square waveform type, the time duration of which is proportional to the instant amplitude of the input signal, that modulation circuit being connected between an output circuit node (P), connected to an output terminal (OUT) of the amplifier, and first (M) and second (N) input circuit nodes, respectively connected to first (IN1) and second (IN2) input terminals of the amplifier for coupling to a signal source, characterized in that a first circuit element (R1) having a predetermined impedance is feedback connected between the output circuit node (P) and the second input circuit node (N), a second circuit element (R2) having a predetermined impedance is connected between the second input circuit node (N) and the second input terminal (IN2), and a capacitive element (C) is connected between the first (M) and the second (N) input node.
- A power amplifier according to Claim 1, characterized in that the first and second circuit elements are resistors and the capacitive element is a capacitor.
- A power amplifier of the two-state type, comprising a differential input stage having first (IN1) and second (IN2) input terminals for coupling to a signal source, and first and second output terminals respectively connected to first (S) and second (R) input terminals of a multivibrator circuit of the bistable type (MVIBR) having at least one output terminal connected to a level-translating output stage (PSW) for the signals generated by the multivibrator circuit, characterized in that a first circuit element (R1) having a predetermined impedance is feedback connected between an output terminal of the level-translating stage and an input circuit node of the differential stage, a second circuit element (R2) is connected between said circuit node and the second input terminal of that differential stage, and a capacitive element (C) is connected between said circuit node and the first input terminal of the differential stage.
- A power amplifier according to Claim 3, characterized in that the first and second circuit elements are resistors and the capacitive element is a capacitor.
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP95830063A EP0730344B1 (en) | 1995-02-28 | 1995-02-28 | Single pole negative feedback for class-D amplifier |
DE69522092T DE69522092T2 (en) | 1995-02-28 | 1995-02-28 | Class D amplifier with single-pole negative feedback |
JP8036515A JPH08265059A (en) | 1995-02-28 | 1996-02-23 | Power amplifier |
US08/607,601 US5796302A (en) | 1995-02-28 | 1996-02-27 | Single pole negative feedback for class-D amplifier |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP95830063A EP0730344B1 (en) | 1995-02-28 | 1995-02-28 | Single pole negative feedback for class-D amplifier |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0730344A1 true EP0730344A1 (en) | 1996-09-04 |
EP0730344B1 EP0730344B1 (en) | 2001-08-08 |
Family
ID=8221860
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP95830063A Expired - Lifetime EP0730344B1 (en) | 1995-02-28 | 1995-02-28 | Single pole negative feedback for class-D amplifier |
Country Status (4)
Country | Link |
---|---|
US (1) | US5796302A (en) |
EP (1) | EP0730344B1 (en) |
JP (1) | JPH08265059A (en) |
DE (1) | DE69522092T2 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2003005570A1 (en) * | 2001-07-03 | 2003-01-16 | Niigata Seimitsu Co., Ltd. | Audio reproducing device and method, audio amplifier, and integrated circuit for audio amplifier |
EP1594225A1 (en) | 2004-05-05 | 2005-11-09 | Monolithic Power Systems, Inc. | Method and apparatus for self-oscillating differential feedback class-D amplifier |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6545533B2 (en) | 2000-12-18 | 2003-04-08 | Texas Instruments Incorporated | Class D audio speaker amplifier circuit with pseudo noise modulation |
DE10300195A1 (en) * | 2003-01-08 | 2004-07-22 | Althoff, Jürgen, Dipl.-Ing. | Low frequency class D vacuum tube amplifier has multivibrator that varies clock output pulse duty cycle according to control voltage so pulse time-voltage area difference varies with input signal |
US7554391B1 (en) | 2008-01-11 | 2009-06-30 | Freescale Semiconductor, Inc. | Amplifier having a virtual ground and method thereof |
US8553909B2 (en) | 2011-04-29 | 2013-10-08 | Smsc Holdings S.A.R.L. | Low-power class D amplifier using multistate analog feedback loops |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3537022A (en) * | 1968-01-10 | 1970-10-27 | Hewlett Packard Co | Signal translating circuit |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4403196A (en) * | 1981-04-22 | 1983-09-06 | The United States Of America As Represented By The Secretary Of The Air Force | Pulse width modulated power amplifier with differential connecting line voltage drop comparators |
US5218315A (en) * | 1992-01-06 | 1993-06-08 | Infinity Systems, Inc. | Switching amplifier |
-
1995
- 1995-02-28 EP EP95830063A patent/EP0730344B1/en not_active Expired - Lifetime
- 1995-02-28 DE DE69522092T patent/DE69522092T2/en not_active Expired - Fee Related
-
1996
- 1996-02-23 JP JP8036515A patent/JPH08265059A/en active Pending
- 1996-02-27 US US08/607,601 patent/US5796302A/en not_active Expired - Lifetime
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3537022A (en) * | 1968-01-10 | 1970-10-27 | Hewlett Packard Co | Signal translating circuit |
Non-Patent Citations (2)
Title |
---|
L. PIERRE: "SORTIES DE PUISSANCE POUR AMPLIFICATEURS OPÉRATIONNELS", ELECTRONIQUE INDUSTRIELLES, no. 22, PARIS FR, pages 37 - 39 * |
P. GEELEN: "SELF-OSCILLATING PWM AMPLIFIER", ELEKTOR ELECTRONICS, vol. 5, no. 9, CANTERBURY GB, pages 9.46 - 9.48 * |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2003005570A1 (en) * | 2001-07-03 | 2003-01-16 | Niigata Seimitsu Co., Ltd. | Audio reproducing device and method, audio amplifier, and integrated circuit for audio amplifier |
US7102426B2 (en) | 2001-07-03 | 2006-09-05 | Niigata Seimitsu Co., Ltd. | Audio reproducing device and method, audio amplifier, and integrated circuit for audio amplifier |
EP1594225A1 (en) | 2004-05-05 | 2005-11-09 | Monolithic Power Systems, Inc. | Method and apparatus for self-oscillating differential feedback class-D amplifier |
Also Published As
Publication number | Publication date |
---|---|
DE69522092D1 (en) | 2001-09-13 |
DE69522092T2 (en) | 2002-04-11 |
EP0730344B1 (en) | 2001-08-08 |
JPH08265059A (en) | 1996-10-11 |
US5796302A (en) | 1998-08-18 |
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